Researchers advance the board engineering pathway to improve power electronics

As global power needs and supply growth continues to accelerate, efficient power electronics to improve grid efficiency, stability, integration and resilience of all energy sources will be key.

Advances in wide bandgap materials in semiconductors offer the potential to allow greater power handling of power electronics while reducing electrical and heat losses. Wide bandgap materials allow for smaller, faster, more reliable, and more energy efficient power electronic components than today’s commercially available silicon-based electronic components.

Researchers from the National Institute of Renewable Energy (NREL), Colorado Mining School, and Oak Ridge National Laboratory have investigated the potential routes to achieve peak performance of ALXGA1-XN, a key material for improving energy efficiency and performance in power electronics through the growth of optimized substrate materials.

The goal of this work is to grow high quality materials by selecting grid matching substrates. Improved transmittance improves device performance, but growth of ALXGA1-XN on substrates, essential for the lattice field, leads to dislocation (line defects that distort the lattice due to atom misalignment), resulting in poor performance.

“Substrate engineering allows for the use of high-performance materials in real devices,” says Dennice Roberts of Materials Science researcher Nrel. “If we can design lattice match substrates to reduce the effects of dislocations, we can broaden the range of sufficiently high-quality materials and build better, more energy-efficient power electronics.”

As detailed in the new paper, “Design of TAC Virtual Substrates for Vertical ALXGA1-XN Power Electronics Devices” was published in PRX Energy, and the researchers proposed and demonstrated that electrically lattice-type carbides (TACs) act as appropriate substrates to meet ALXGA1-XN epigynees.

Advantages of transition metal carbides for ALXGA1-XN growth

Board engineering can improve device performance, but it is complicated. Defects such as substrate cracks are common in ALN ​​and GAN growth. Efforts to reduce dislocations have been effective, but often increase device complexity and limit device design and performance. Lattice mismatches again lead to device performance issues.

“Grid matching is important for the growth of high-quality epitaxials,” Roberts said. “Not only for ideal lattice matching, but the TAC and ALXGA1-XN are approaching the lattice state, and the TAC is very conductive and depicts matching growth.

The team grew, prepared and used TAC thin films as virtual substrates for high aluminium-containing ALXGA1-XN, demonstrating ALXGA1-XN growth with TAC virtual substrates. To accurately and effectively deposit TAC on the substrate, they used radio frequency sputtering. They formed the substrate via high temperature annealing. This is a process that increases ductility, that is, to increase the ability of a metal to undergo significant stress before cracking or breaking, reducing defects.

The rational design of heterostructure interfaces enables new device concepts

Motivated by the work of Roberts and her co-authors, Sharad Mahatara, a postdoctoral researcher in NREL materials science, and Stephen Lani, a senior scientist at NREL, approached the problem of interfaces between materials with different crystal structures from a computational perspective.

Their study, “Heterostructural Interface Engineering for Ultrawave Gap Nitrides from First Principles: TAC/ALN and TAC/GAN ROCKSALT-WURTZITE Interfaces,” was recently published in the Physical Review Applied. The broader context of this study is that lattice match substrates with the same crystal structure are often unavailable. Therefore, if we can understand and control the formation of these more complex interfaces, there is a new opportunity to use heterostructured interfaces for transformation and control.

Formation of interfaces between Rocksalt structure (RS) and Wurtzite structure (WZ) materials – Between EG, TAC and ALN (GAN) films, can be modeled by considering the various possibilities of stacking individual atomic layers. This problem is related to some degree to the question of how to place oranges in a box to put as much as possible.

Researchers at NREL approached this problem by using algorithms to create computer code to systematically enumerate possible stacking sequences within several atomic layers near the interface. This algorithm can be used to understand the atomic structures of a variety of corresponding RS/WZ interfaces, including oxide interfaces.

Mahatara and Rani then use first-principles density functional theory calculations to determine the most energetically stable atomic structural arrangement of substrate termination (the final substrate atomic layer, type of TA or C), film nucleation (the first nitride film layer, AL/GA or N), and WZ PORICATION (describes AL/GA or N PORS).

Furthermore, they used this data to predict which of the combinations would have the most advantage under different experimental synthesis conditions. This information is important as the detailed atomic structure of the interface determines the function and performance of the material in the device.

For example, polarity affects the electric field involved in the transport of electrons across the interface. Therefore, controlling the polarity of the growing film is an important aspect of argan epitaxy.

“Our results may guide experimenters on how to modulate nitrogen polarity against the metal polarity of nitride films grown on TAC substrates as a function of growth conditions,” Mahatara said.

As a follow-up to the current work, Mahatara and Rani are currently investigating the electronic properties of the predicted structure. This ongoing effort provides further information and predictions about how these structures act and implement in the new device concept. The goal is to provide experimenters with critical data on rational device designs to accelerate the development of new concepts in microelectronics.

Findings from both studies may inform substrate engineering that improves power electronics as the needs of electrification futures grow.

“We are excited about the possibility that these materials will address the challenges of electricity and energy efficiency,” Roberts said. “From a research perspective, it’s really nice to see creative solutions to long-standing problems. It looks like there are many promises in real-world applications, so I look forward to future developments.”